Light-emitting element and display device using same

ABSTRACT

A display device includes a plurality of light-emitting elements aligned on a TFT substrate in a formation of a matrix. The plurality of light-emitting elements each have a flat surface portion and including a light-emitting layer, an anode, and a cathode, an insulating layer formed on the TFT substrate and under the light emitting element, and a tilted metal surface provided on a peripheral area surrounding the flat surface portion of the light-emitting element and having a tilt angle with respect to the flat surface portion of the light-emitting element. The tilted metal surface is provided on a surface of a slope of a bank that is provided on the insulation layer, and a width of a cross-section of the bank becomes smaller as the cross section comes farther away from a surface of the TFT substrate. A counter substrate is placed on the TFT substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 14/327,098,filed Jul. 9, 2014, which is a continuation of application Ser. No.14/045,162, filed Oct. 3, 2013, now U.S. Pat. No. 8,791,632, which is acontinuation of application Ser. No. 13/477,590, filed May 22, 2012, nowU.S. Pat. No. 8,558,449, which is a continuation of application Ser. No.13/206,915, filed Aug. 10, 2011, now U.S. Pat. No. 8,193,697, which is acontinuation of application Ser. No. 12/631,326, filed Dec. 4, 2009, nowU.S. Pat. No. 8,049,405, which is a continuation of application Ser. No.11/852,153, filed on Sep. 7, 2007, now U.S. Pat. No. 7,812,515, which isa continuation of application Ser. No. 11/361,298, filed on Feb. 23,2006, now U.S. Pat. No. 7,279,833, which is a continuation ofapplication Ser. No. 10/653,623, filed on Sep. 2, 2003, now U.S. Pat.No. 7,030,556, and claims the benefit of priority under 37 CFR 119 ofJapanese application no. 2002-360283, filed on Dec. 12, 2002, all ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a light-emitting element and a displaydevice that presents picture images by controlling the light-emissionoperation of the light-emitting element, especially, to a technologythat can be effective to such a light-emitting element as an organiclight-emitting diode and to a display device equipped with the organiclight-emitting diode.

BACKGROUND OF THE INVENTION

An organic light-emitting diode (abbreviated as OLED hereinafter) is adevice that converts electric energy to light energy by injecting holesand electrons to a light-emitting layer constructed with an organic thinlayer. A display device constructed with OLED (abbreviated as OLEDdisplay, hereinafter) is thin and lightweight because no additionallight as backlight is required due to the self light-emittingcapability. Furthermore, OLED displays have other features such as wideviewing angle and quick time-response in display characteristics.

FIG. 33 shows an example of an OLED construction and a substantialsectional view of the drawing that explains the display operation. ThisOLED is constructed with transparent electrode 200 functioning as ananode, hole transporting layer 103, light-emitting layer 102, anelectron transporting layer 101, a reflective electrode 300 made oflight-reflective metal that functions as a cathode on a transparentsubstrate 400, layered in this order. Once a DC voltage is appliedbetween the transparent electrode 200 and the reflective electrode 300,the holes injected through the transparent electrode 200 travel in thehole transporting layer 103, and the electrons injected through thereflective electrode 300 travel in the electron transporting layer 101.Both holes and electrons reach the light-emitting layer 102 whereelectron-hole recombination occurs and a light with a certain wavelength is emitted. A part of the light emitted from the light-emittinglayer 102 is observed through the transparent substrate 400 by a viewer1000. The light emitted roughly parallel to the boundary surface of thelayers or the light that has a larger incident angle against theboundary surface than the critical angle between the two layers thereof,is propagated in parallel to the boundary surfaces, does not travel tothe viewer and therefore they are not effectively used for displaylights. The external coupling efficiency (the ratio of the amount oflight extracted to the viewer 1000 and the emitted light from thelight-emitting layer 102, or the ratio of the external quantumefficiency to the internal quantum efficiency) is generally estimated tobe about 20% based on classical ray optics. The large amount of lightgenerated at the light-emitting layers that travel in parallel to theboundary surface of the layers becomes a loss in the display system.Therefore, in order to realize low consumption power and a bright OLED,it is desirable to reduce the light guiding loss and to raise theexternal coupling efficiency.

The references as Patent 1 and Patent 2 shown below describe OLEDs thathave reflection surfaces with tilted surfaces in order to reduce theguiding loss. For these cases, the description says the light emittedfrom the light-emitting layers travels in parallel or substantiallyparallel to the substrate or the layered film, is reflected at thetilted reflective surface and changes the traveling direction, whichresults in the reduction of light guiding loss and improvement of theexternal coupling efficiency.

REFERENCES

Patent 1: JP laid-open publication 2001-332388

Patent 2: JP domestic publication 2001-507503

FIG. 34 shows a cross sectional view of an example of OLEDs. As shown inFIG. 34, a portion of the light which is emitted from the organic layer100, including the light-emitting layer, travels in parallel orsubstantially parallel to the substrate is reflected at the tiltedreflective surface (shown as the tilted surface of the electrode 300)and then the propagation direction is closed to the viewer 1000. Howeverthe light that is emitted from the light-emitting layer and incident tothe tilted reflective surface is a part of the light emitted from thelight-emitting layer; therefore, a large part of the light is still lostand not effectively used. Furthermore, a portion of the light emittedfrom a pixel of the light-emitting layer is not incident upon the tiltedreflective surface and travels into a different pixel, then incident tothe tilted reflective surface formed in a different pixel and changingthe direction to the viewer. This may cause an optical cross-talk and ablur of the display. Furthermore, as shown in FIG. 34, when the tiltedreflective surface is used as an electrode for an element of OLED,disconnection occur at the electrode step levels over the tiltedreflective surface.

To solve various problems as described above the light emitted from thelight-emitting layer contributes much to the display light and realizesa bright display such that a high quality picture is provided as no bluris generated. Furthermore, other objectives of this invention are toprovide fault free OLED that has no disconnection failure. The otherpurposes of this disclosure will be clarified in the followingdescriptions.

SUMMARY OF THE INVENTION

In order to achieve the above purposes, the display device havingplurality of light-emitting elements that construct picture elementsaligned on a substrate in a formation of a matrix, wherein thelight-emitting element comprising a flat surface of a light-emittinglayer made at least in a portion therein and a tilted reflective surfaceat least in a portion therein, of which the tilted reflective surface ismade in the peripheral areas surrounding said surface of alight-emitting layer and has a tilt angle against the flat surface,wherein an optical waveguide layer is filled in an area surrounded bysaid tilted reflective surface on said light-emitting layer by whichlight generated at said light emitting layer is guided to the peripheralareas and wherein the optical waveguide layer is optically isolated fromeach picture element by the tilted reflective surface. Furthermore, thetilted reflective surface is on the surface of a slope formed by a bankthat is on said substrate wherein cross sectional width of the bank isnarrower against distance farther from surface of the substrate,therefore the optical waveguide layer has across sectional formation asa cross sectional width of the optical waveguide layer is wider againstdistance farther from a surface of the substrate.

In order to realize an optical waveguide layer that is opticallyisolated from the other picture elements, the height of the tiltedreflective surface from the flat surface of the light-emitting layer islarger than the maximum height of the optical waveguide layer. In someembodiments, the optical waveguide layer is formed in a construction asthe optical waveguide layer is isolated from the other optical waveguidelayers for each picture element.

In an embodiment, the light-emitting element includes an organiclight-emitting diode constructed with a reflective electrode configuredas an optical reflector, a light-emitting layer comprising an organiclayer and a transparent electrode stacked in order from the substrate.In an embodiment, the refractive index of the optical waveguide layer islarger than that of the air, and lower than that of the transparentelectrode. Furthermore, a sealing material that is transparent againstvisible light and has gas barrier characteristics is set on a side ofthe light-emitting layer made on the substrate, wherein the substrateand the sealing material are adhesively bound with a gap that hassubstantially the same refractive index as the air.

In an embodiment, the light emitted from the light-emitting layertravels into the optical waveguide layer or passes through thetransparent electrode after reflecting on the reflective electrode. Apart of the light, among the light incident to the boundary between theoptical waveguide layer and the air gap (we call the surface of theoptical waveguide layer, hereinafter), is reflected with the smallerincident angle than the critical angle; however, most of the lighttravels to the viewer and passes through the air gap and the sealingmaterial. On the other hand, the part of the light, among the lightincident to the optical waveguide layer, which has a larger incidentangle to the surface of the optical waveguide layer is totally reflectedat the surface of the optical waveguide layer, and travels within theoptical waveguide layer in parallel to the substrate. The lighttraveling in the optical waveguide layer approaches the tiltedreflective surface and the propagation direction is changed by thereflection thereon; and the light that is incident to the surface of theoptical waveguide layer with a smaller incident angle than the criticalangle partially propagates towards the viewer and is effectively used asthe display image light.

In an embodiment, the light guided in parallel to the substrate and isregarded as light loss in conventional technologies, is guided to thetilted reflective surface in a good efficiency and the light extractingratio is improved. In this embodiment, since the optical waveguide layeris at least isolated from each other by each picture element, the lightemitted from the light-emitting layer is not guided to the differentpicture elements. Thus, a display with high picture-quality is realizedwithout degrading picture-quality seen in optical cross-talk or blur.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross sectional view of a picture element of the firstembodiment of the display device.

FIG. 2 is a plan view of the first embodiment of the display device.

FIG. 3 is a cross sectional view of an example of operation of the firstembodiment of the display device.

FIG. 4 is an explanatory schematic that shows the estimation of theviewing angle characteristics of the light intensity against the slopeangle α.

FIG. 5 is an explanatory schematic of the light traveling in the opticalwaveguide layer when the refractive index of the optical waveguide layeris smaller than that of the transparent electrode.

FIG. 6 is an explanatory schematic of the light traveling in the opticalwaveguide layer where the refractive index of the optical waveguidelayer is larger than that of the transparent electrode.

FIG. 7 is a block diagram showing the whole layout of the embodiment ofthe display device.

FIG. 8 is an equivalent circuit diagram of the active matrix of thedisplay device shown in FIG. 7.

FIG. 9 is a layer drawing of the picture element of the embodiment ofthe display device.

FIG. 10 is a cutaway view along 8-8 line shown in FIG. 9

FIG. 11 is a timing chart of the applied voltage to the gate line.

FIG. 12 is an explanatory schematic of an example of voltage statusamong the gate voltage, the data line voltage and the voltage in thestorage capacitor.

FIGS. 13A-13D schematically show the process to fabricate the bank ofthe display device.

FIG. 14 is a schematic view of the bank of the display device.

FIGS. 15A-15C schematically show the process to fabricate the organiclayer of the device.

FIGS. 16A-16C schematically show the process to fabricate the opticalwaveguide layer of the device.

FIG. 17 is a cross sectional view of a picture element of the secondembodiment of the display device.

FIG. 18 is a schematic view of the effect of the optical waveguide layerin the second embodiment.

FIG. 19 is another schematic view explaining the effect of the opticalwaveguide layer in the second embodiment.

FIG. 20 is a cross sectional view of a picture element of the thirdembodiment of the display device.

FIG. 21 is a cross sectional view of a picture element of the fourthembodiment of the display device.

FIG. 22 is a cross sectional view of a picture element of the fifthembodiment of the display device.

FIG. 23 is a cross sectional view of a picture element of the sixthembodiment of the display device.

FIGS. 24A-24C schematically show the fabrication process of the displaydevice regarding the sixth embodiment shown in FIG. 23.

FIGS. 25A-25C schematically show the fabrication process of the displaydevice regarding the sixth embodiment shown in FIG. 23.

FIG. 26 is a cross sectional view of the picture element of the sixembodiment of the display device.

FIG. 27 is a plan view of a picture element of the seventh embodiment ofthe display device.

FIG. 28 is a cutaway view along C-C line shown in FIG. 27.

FIG. 29 is a cutaway view along C-C line shown in FIG. 27 where theembodiment shown in FIG. 23 is applied to embodiment shown in the FIG.27.

FIG. 30 is a cross sectional view of a picture element or the eighthembodiment of the display device.

FIG. 31 is a plan view of a picture element of the eighth embodiment ofthe display device.

FIG. 32 is across sectional view of a picture element of the ninthembodiment of the display device.

FIG. 33 is a schematic shown an example of the construction and thedisplay operation regarding an OLED.

FIG. 34 schematically shows an example of a cross sectional view of anOLED.

PREFERRED EMBODIMENT OF THE INVENTION

Hereinafter, exemplary embodiments will be discussed in conjunction withthe drawings as needed.

The First Embodiment

FIG. 1 shows the cross sectional view of one picture element explainingthe first embodiment. FIG. 2 shows another drawing explaining the firstembodiment. FIG. 1 corresponds to the cutaway view along the line of A-Ain FIG. 2. One color picture element includes three picture elements ofred-light-emitting picture element 20R, green-light-emitting pictureelement 20G and blue-light-emitting picture element 20B, which arearranged in side-by-side as shown in FIG. 2 and the predetermined coloris presented by additive color mixing of the lights emitted from thesethree picture elements. In addition, these picture elements 20R, 20G and20B are called unit picture elements or sub-pixels, and a unit pictureelement corresponds to a mono-chromatic picture element for the case ofmono-chromatic display device.

For the display device, wires, switching elements, storage capacitorsand insulating layers are formed on the substrate as appropriate, eventhough they are not shown in the drawings. Reflective electrodes 300include conduction material with optical reflecting characteristics thatare formed on the substrate in an island shape as corresponding to thepicture element, and banks 500 made of insulator material are formed tothe edges of reflective electrodes 300 at the peripheral areas thereof.The bank 500 has a cross sectional formation in a shape as the width isgetting narrow as getting farther from the substrate 800 and has tiltedsurfaces at its side areas. On the part of the tilted surface and thereflective electrode, an organic layer 100 that includes thelight-emitting layer formed in each picture element in a form of anisland and a transparent electrode 200 is formed thereon.

The transparent electrode 200 and the reflective electrode 300 areconfigured as an anode (or cathode) and a cathode (or anode),respectively and include an organic light emitting diode with an organiclayer 100 formed on these electrodes. The organic layer 100 isconstructed in three layered forms, as an electron transporting layer, alight-emitting layer and a hole transporting layer in order from thecathode side, or in two layered form, as a single layer functioning aslight-emitting and electron transporting by using a material of dualuse. Furthermore, in an embodiment, the organic light emitting diode,includes an additional anodic buffer layer between the anode and thehole transporting layer.

A tilted reflective surface 700 including of optical reflective metal isformed on the transparent electrode 200 at the location corresponding tothe surface of a slope formed by a bank 500. Furthermore, an opticalwaveguide layer 600 is transparent to visible light and includes amaterial that has a larger refractive index than that of air, and isfilled in the basin-like area surrounded by the tilted reflectivesurface 700. Moreover, since the organic layer 100 is usually degradedby the moisture included in the air, in an embodiment, organic layer 100is sealed by a seal-off means from the open air so that it is notexposed to the open air. In this embodiment, bank 500 is a as spacer,and a seal-off material 900 and the substrate 800 are fixed by anadhesive seal material cemented in a frame-like form around the displayportion of the display device.

A glass plate, a plastic film post-processed for gas barrier or alayered plate with thin glass and plastic film can be used for theseal-off material 900. For this construction, it is important to set agap 950 which has the similar refractive index to the air between theseal-off material 900 and the optical waveguide layer 600. Because ifthe seal-off material 900 and the optical waveguide layer 600 contacteach other, then the light emitted from the organic layer 100 andpropagating in the optical waveguide layer 600 comes into the seal-offmaterial 900 and does not come up to the viewer 1000, resulting in aloss or travels into other picture element, and comes up to the viewer1000 thereafter as resulting into, problems of cross-talk and blur.

Inert gas as nitrogen gas may be enclosed in the gap 950, and theassembly is performed as nitrogen gas is enclosed and the seal-offmaterial and the substrate 800 are bound in air-tight. Furthermore, inan embodiment, setting gap 950 is configured such that the opticalwaveguide layer 600 does not contact the seal-off material 900, and gap950 should be set larger than the distance over which the light cannottravel from the optical waveguide layer 600 to the seal-off material 900(due to the tunneling phenomenon of photons). Since the tunnelingphenomenon occurs for a gap shorter than the wavelength of visiblelight, in an embodiment, the gap 950 is more than 1 μm.

Moreover, in some embodiments, it is important to keep the height H2(from a flat surface 25 of the organic light emitting diode) from thereflective electrode 300 to the optical waveguide layer 600, smallerthan the height H1 at the upper end of the tilted reflective surface700. The reason is from optical cross-talk and blur that are caused bylight emitted from the organic layer 100 traveling in the opticalwaveguide layer 600 may propagate over the tilted reflective surface 700when the height H2 of the optical waveguide layer 600 is larger than theheight H1 of the tiled reflective surface 700, and invade into differentpicture elements and then externally travel therefrom. Furthermore, forembodiments when the flat seal-off material 900 is set as the bank 500used as a spacer, the optical waveguide layer 600 contacts the seal-offmaterial 900 unless H1>H2 is kept then the light invading from theoptical waveguide layer 600 to the seal-off material 900 causes problemsas reduction of the external coupling efficiency, optical cross-talk andblur.

FIG. 3 is a cross sectional view of an example of operation for thefirst embodiment of the display device. Once DC voltage is applied tothe transparent electrode 200 and the reflective electrode 300 inresponse to the picture signal, the holes injected through the anodetravel in the hole transporting layer and electrons injected through thecathode travel in the electron transporting layer, respectively, andboth holes and electrons reach the emitting layer. The recombination ofan electron and a hole occurs in the emitting layer and light emissionoccurs. The light emitted from the light emitting layer that constructsthe organic layer 100 comes into the optical waveguide layer 600 throughthe transparent electrode 200 as is emitted or after reflected at thereflective electrode 300. The lights, among the lights coming into theoptical waveguide layer 600, that come to the boundary between theoptical waveguide layer 600 and the gap 950 with a smaller incidentangle than the critical angle is partially reflected but most of thereflected light travels up to the viewer, after passing through the gap950 and the seal-off material 900 which is not shown, and are used asdisplay image lights 2000.

On the other hand, the light travelling onto the surface of the opticalwaveguide layer 600 with a larger angle than the critical angle istotally reflected at the surface of the optical waveguide layer 600 andpropagates in the optical waveguide layer 600 in parallel to the surfaceof the substrate 800. The light traveling in the optical waveguide layer600 approaches the tilted reflective surface 700, and the direction ofpropagation changes by the reflection; a part of the light that comesinto the surface of the optical waveguide layer 600 with a smallerincident angle than the critical angle travels to the viewer and iseffectively used as display image light 2001. In other words, the lighttraveling in parallel to the substrate 800 which results in a loss inconventional technology, but in the embodiment, is led to the tiltedreflective surface 700 by the optical waveguide layer 600 and changesthe propagation direction by the reflection at the tilted reflectivesurface 700. Then, since the light is effectively used as the displayimage light, the external coupling efficiency has been improved. Forthis case, since the optical waveguide layer 600 is completely isolated,the light emitted from an organic layer of a certain picture elementdoes not propagate in other different picture elements and opticalcross-talk or blur of presentation occurs.

The improvement of the external coupling efficiency by suppressing thelight loss due to above the propagation increases as the ticker opticalwaveguide layer in comparison to the area of the light-emitting portionis made. In other words, though the portion of the flat surface 25 isthe light-emitting area, the thicker the optical waveguide layer 600 is,the higher the external coupling efficiency can be.

The light guided in the optical waveguide layer 600 mainly travels tothe tilted reflective surface 700 with repeating the reflection at thesurface of the optical waveguide layer 600 and that at the reflectiveelectrode 300. For this case, since the reflectance of the reflectiveelectrode 300 is not 100%, usually, the light is partially absorbed andlost by the reflective electrode. Therefore, if the number of times thereflection at the reflective electrode 300 until the light in theoptical waveguide layer 600 comes to the tilted reflective surface 700can be reduced, the optical loss by the reflective electrode 300 becomesless and high efficiency of the light extraction from the display can beobtained. Moreover, since no guiding of the light in the opticalwaveguide layer can provide no improvement of external couplingefficiency, the thickness of the optical waveguide layer should belarger than the wavelength of the light so that the good propagation ofthe light is obtained. In an embodiment, the thickness of the opticalwaveguide layer is larger than 1 μm.

As shown in FIG. 2, if the length H in the up-down orientation is longerthan the length W in the left-right orientation in the plane of theemitting area, then the relation as (H2/W)>(H2/H) is obtained. In thisembodiment, the external coupling efficiency for the left-rightorientation is greater than that for the up-down orientation and theviewing angle is wider in the right-left orientation than in the up-downorientation. The wider viewing angle in the right-left orientation ispreferred than that of the up-down orientation, and the limited lighthas to be provided to the viewers. In other words, the conventional OLEDdisplays have has an isotropic viewing angle for the light intensitywhich is uniform for every direction; however, an embodiment can controlthe viewing angle characteristics of the light intensity by controllingthe ratio of the thickness of the optical waveguide layer to the lengthof the light emitting area for the specific orientation. Therefore, wecan realize the optimum light intensity characteristic for eachparticular application of the display devices.

The viewing angle characteristics against the light intensity can becontrolled by the tilt angle .alpha. of the tilted reflective surface700 against the surface (substrate surface) that is a flat surface 25 inon embodiment. FIG. 4 shows the schematics diagram of the viewing anglecharacteristics against the light intensity as a function of the tiltangle α of the tilted reflective surface 700. FIG. 4 is provided for thecase of the ratio H2/W=0.1 for the length W (see FIG. 2) of the lightemitting area and the thickness H2 of the optical waveguide layer 600(see FIG. 1) and the refractive index 1.5 for the optical waveguidelayer and shows the estimation results for a two-dimensional model. Thehorizontal axis shows the viewing angle and the vertical axis shows therelative light intensity normalized to the light intensity obtained atthe front position (intensity at 0° viewing angle) by the conventionalOLED that has a flat and plane layered construction. As shown in thisdiagram, the viewing angle characteristics of the light intensity can bechanged by changing the tilt angle α. For example, we can see a highlight intensity at the front direction and the adjacent direction isobtained for α=23°˜30°, almost constant light intensity characteristicsfor wide range of viewing angle for α=45°, and the viewing anglecharacteristics decreasing over a 50° viewing angle for α=60°.

The tilted reflective surface is not the slope surface constructed in acomplete flat surface for actual cases, the tilt angle α tends not to beconstant over the tilted reflective surface and to constantly vary inaccordance with the location of the tilted reflective surface.Therefore, in applications where the display device is used in portablephones, which a single person mostly uses at a time, wide viewing angleis not required, but high intensity at the front direction is preferred.Therefore, in the embodiments, the average angle values for the tiltangle α should be about as 20° ˜30°, and the higher intensity at thefront orientation in comparison to the inclined orientation against thefront orientation. However, in embodiments where the wider viewing angleand the brighter picture image are utilized, with the average value of aapproximately equal to 45° for TV set applications, where the display iswatched by many people. In addition, since the present estimation is thecalculated result provided in a limited condition under a simpletwo-dimensional model, the result is not be used for an exactquantitative evaluation, but is effective as a relative evaluation for aqualitative study.

Next, we explain the relation between the refractive indices of opticalwaveguide layer 600 and transparent electrode 200. FIG. 5 and FIG. 6 arethe schematics to explain the effect against the external couplingefficiency. FIG. 5 is where the refractive index of the opticalwaveguide layer is smaller than that of the transparent electrode, andFIG. 6 is when the refractive index of the optical waveguide layer islarger than that of the transparent electrode. Once we define therefractive index of the transparent electrode n1, that of the opticalwaveguide layer n2, incidental angle θ1 of the light from thetransparent electrode to the optical waveguide layer and refractionangle θ2, we obtain sin θ1/sin θ2=n2/n1 from Snell's law. Therefore,when the refractive index n1 of the optical waveguide layer 600 issmaller than the refractive index n2 of the transparent electrode, therefraction angle θ2 is larger than the incident angle θ1.

On the other hand, when the refractive index n1 of the optical waveguidelayer 600 is larger than the refractive index n2 of the transparentelectrode, the refraction angle θ2 is smaller than the incident angleθ1. Therefore, if we define the propagation distance without reflectionin the optical waveguide layer 600 as L1 when n1>n2 and L2 for n1<n2,then L1 is larger than L2. The fact that the propagation length withoutreflection of the light traveling in the optical waveguide layer 600 islong implies that the times of reflection at the reflective electrode300 until the light traveling up to the tilted reflective surface 700,means the light loss of the absorption by the reflective electrodebecomes less. For this reason, in some embodiments, the refractive indexof the optical waveguide layer is less than that of the transparentelectrode for the purpose of improving the external coupling efficiency.It should be noted that a critical angle exists between the transparentelectrode 200 and the optical waveguide layer 600, and the light with alarger incident angle from the transparent electrode to the opticalwaveguide layer is totally reflected and is not transmitted to theoptical waveguide layer 600.

In contrast, the critical angle does not exist for the case of n1<n2,therefore the incident angle which even becomes to be the critical anglefor the case of n1>n2, the light is transmitted from the transparentelectrode to the optical waveguide layer. However, since such a light istotally reflected at the surface of the optical waveguide layer 600 andreturns back to the reflective electrode 300, the light is repeatedlyreflected by the surface of the optical waveguide layer 600 and thereflective electrode 300, and is lost by the attenuation. To preventthis phenomenon, it is necessary to increase the thickness of theoptical waveguide layer by which the number of reflections of the lightat the reflective surface 300 can be reduced, until the light reachesthe tilted reflective surface 700 while traveling in the opticalwaveguide layer. However, in general, the refractive index of thetransparent electrode 200 is rather high as 1.8 to 2.2 and it takes along time to form a transparent material (titanium oxide, for instance)that has a larger refractive index than this in a thickness of an orderof micron meters without damage to the organic layer therefore suchformation is not industrially practical. Therefore, it is desirable thatthe refractive index of the optical waveguide layer should be largerthan that of air, and less than that of the transparent electrode, andthe optical waveguide layer is made of a transparent plastic materialthat is relatively formed in ease. In some embodiments, the refractiveindex of the optical waveguide layer is 1.3 to 1.7.

Next, we explain an embodiment of the display device with reference tothe schematics. FIG. 7 shows a schematic of the whole layout of theembodiment. FIG. 8 is an equivalent circuit of the active matrixconstructed on the display portion 2. As shown in FIG. 7, the displaydevice 1 has a display portion 2 at substantially the center of thesubstrate 800. In this display portion 2, a data driver circuit tooutput the picture signals to a plurality of data lines 7 is constructedin the upper part of the display portion and a scan driver circuit tooutput the scan signals to a plurality of gate lines 8. The drivercircuits 3 and 4 comprise shift register circuits, level shiftercircuits and analog circuits which include P channel and N channel TFTs(Thin Film Transistors) in a complementary configuration. The line 9 isa common voltage line.

In an embodiment, display device 1 is similar to active matrix liquidcrystal display devices such that a plurality of gate lines and datalines cross each other in the direction of the expansion, and thepicture element 20 is located at each cross point of gate lines G1, G2,. . . , Gm and data lines 01. 02, . . . , On. Each picture elementincludes a light-emitting element 24 including an OLED, storagecapacitor 23, a switching transistor 21 of an N channel TFT of which thegate electrode is connected to the gate line, either a source or a drainelectrode is connected to the data line and the other is connected tothe storage capacitor 23, and a driver transistor 22 of an N channel TFTof which the gate electrode is connected to the storage capacitor 23,the source electrode is connected to the common voltage line 9 extendingin the same direction as the data lines and the drain electrode isconnected to the cathode of an OLED that is the light-emitting element24. Moreover, the anode of an OLED of a light-emitting element 24 isconnected to a current supply line commonly used for all pictureelements and kept at the same voltage Va. The light-emitting element 24emits any of red-, green- or blue-lights and is aligned in apredetermined order in a matrix formation.

In the above construction, once the switching transistor 21 is in an“ON” state, then the picture signal is written in the storage capacitor23 through the switching transistor 21. Therefore, the gate electrode ofthe driver transistor 22 is kept at a voltage corresponding to thepicture signal by the storage capacitor 23 even if the switchingtransistor 21 is set to “OFF” state. The driver transistor 22 is kept ina source follower mode which features constant current characteristicsand the light-emitting operation is maintained since the current fromthe current supply line flows to the organic light-emitting diode thatforms the light-emitting element 24. For this embodiment, the intensityof the emitted light depends on the data written in the storagecapacitor 23. The cease of the emission is realized by setting thedriver transistor 22 “OFF” state.

We explain the construction of the display device regarding the firstwhile referring to a combination of FIG. 9 and FIG. 10 and that of FIG.1 and FIG. 2. FIG. 9 is a layer drawing of the picture element showingthe constructing layers. FIG. 10 shows a cutaway view along the line B-Bin FIG. 9. The display device in this embodiment is constructed includethat driver elements (thin film transistors in this embodiment) includeswitching transistors and driver transistors and elements connected tothose driver elements as gate lines, data lines, a common voltage lineand storage capacitor, are formed on a flat substrate 800 as glass andinsulation layer 30 is formed thereover. On the insulation layer 30, areflective electrode 300 that functions as a cathode of thelight-emitting element 24 is formed in a shape of an island and thereflective electrode 300 is connected to the drain electrode 26 of thedriver transistor by a contact hole 31 opened in the insulation layer30.

In this embodiment, the reflective electrode 300 functions as a cathode.For the cathode, the metals of low work function as aluminum, magnesium,magnesium-silver alloy; aluminum-lithium alloy, etc. can be used. Sincethe configuration of a single metal layer using aluminum needs highdriving voltage and the life-time of the display device is short, aultra-thin film of Li compound (as lithium oxide Li2O, lithium fluorideLiF) formed between the reflective electrode and the organic layer maybe used which equivalently functions as aluminum-lithium alloy.Alternatively, the cathode surface contacting the organic layer is dopedwith a high reactive metal such as lithium or strontium and then the lowdrive voltage is obtained. In some embodiments, the reflective electrodeis made of highly optical reflective material in order to obtain thehigh usage efficiency of the light for viewing image.

In the area on which driver elements and signal lines are formed, a bank500 which overlays these elements and lines, and surrounds the flat areaof the reflective electrode 300 is formed thereon. In this embodiment,the bank 500 is formed to cover the contact hole 31. In other words, thecontact hole is aligned and formed underneath the bank. This helps torealize higher intensity of light emission because a step differenceexists on the contact hole 31 resulting in a no use area against lightemitting area and the wider light-emitting area is obtained by arrangingthe no light emitting area under the bank area. Moreover, in someembodiments, the bank is formed to overlay the peripheral part of thereflective electrode 300. Because the organic layer 100 and thetransparent electrode 200 are cracked by the step difference of thereflective electrode 300 at the peripheral part such that thetransparent electrode 200 is electrically broken and/or the reflectiveelectrode 300 and the transparent electrode 200 are electricallyshorted. Instead of these problems, the overlay forming of the bank,therefore, prevents such incidental troubles.

The bank 500 can be formed by patterning an insulator material withphotolithography technology. Inorganic material such silicon oxide,silicon nitride or dielectric material such as acrylic resin andpolyimide resin may be used. In addition, in some embodiments, theheight of the bank is more than a few micron meters in order to realizehigh external coupling efficiency since the dimension of the bank 500determines the height of the tilted reflective surface 700 and thethickness of the optical waveguide layer 600. The organic material isused for the dimensional height of the bank formed in a short timeprocessing. The cross sectional view of the bank 500 has a trapezoidalshape so that the horizontal width is less while the height is fartherfrom the substrate and the side surfaces of the bank has an arrangementinto a tilted surface against the substrate surface. Moreover, the bank500 may be made by other processes to form the designed tilted surfaceusing a screen printing method or a direct printing such as the ink-jetprinting.

The organic layer 100 has a light-emitting layer that emits each of red,green and blue lights is patterned in each predetermined position foreach picture element in a shape of an island. A transparent electrode200 functioning as an anode is formed over the display portion 2. Thetransparent electrode material that has a high work function includes,for example, ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide).

The transparent electrode 200 is connected with the current supply line.For the organic layer 100, a material that emits the light in a designedcolor is used and the construction of three layers includes an electrontransporting layer, a light-emitting layer and a hole transporting layeror two layers includes a material which supports both a light-emittinglayer and an electron transporting layer and a hole transporting layer.

In some embodiments, a red light emitting material includestriphenyldiamine derivative TPD(N,N′-bis(3-methylphenyl)-N,N-diphenyl-[1,1′-biphenyl]-4,4′-diamine) orα-NPD (4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl) andDCM-1(4-dicyanomethylene-6-(p-dimethylaminostyryl)-2-methyl-4-H-pyran)distributed Alq3 (tris(8-quinolinolate)aluminum) for the electrontransporting light-emitting layer (dual usage for an electrontransporting layer and a light emitting layer).

In some embodiments, a green light emitting material includestriphenyldiamine derivative TPD or α-NPD for hole transporting layer andAlq3 or quinacridon-doped Alq3 or Bebq (bis(8-hydroxyquinolinate)beryllium) for the electron transporting light-emittinglayer (dual usage for an electron transporting layer and a lightemitting layer).

In some embodiments, a blue light emitting material includes TPD, α-NPDfor the hole transporting layer and DPVBi(4,4′-bis(2,2-diphenylvinyl)biphenyl) or a material consisting of DPVBiand BCzVBi (4,4′-bis(2-carbazolevinylene)biphenyl) or a material dopedwith distyrylallylene derivative as a host and distyrylamine derivativeas a guest for the light emitting layer and Alq3 for the electrontransporting layer. In some embodiments,Zn(oxz)2(2-(0-hydroxyphenyl)-benzoxazole zinc complex) is/used for theelectron transporting light emitting layer (dual usage for an electrontransporting layer and a light emitting layer).

Moreover, we can use materials of polymer system instead of the abovematerial of a low molecular-weight system. In some embodiments, for thepolymer base materials, we can use multiple-layer film of PEDT/PSS (amixed layer of Polyethylene dioxy thiophene and Polystyrene sulphonate)and PPV (poly(p-phenylene vinylen)) for the hole transporting layer andthe light emitting layer. In some embodiments, we can use green inkblended PPV for green color light emission, rhodamine 101 blended greenink as a dopant for red-color light emission and F8(Poly(dioctylfluorene)) for a blue color light emitting layer. Inaddition, F8 can function as an electron transporting layer. In someembodiments, we can use dye containing polymer such as PVK(poly(N-vinylcarbazole)). In some embodiments, each layer of themultiple layer film is on the order of several tens of nano meters whichis less than the wave length of light.

In some embodiments, for the pattering of the organic layer 100 in eachpredetermined position for each picture element in a fashion of anisland, we can use a published technology as pattered-film formingtechnology used for deposited organic layer through shadow masks (forinstance, S. Miyaguchi, et al.: “Organic LED Fullcolor Passive-matrixdisplay”, Journal of the SID, 7, 3, pp 221-226 (1999)). In this process,the bank 500 can be used as a spacer of the shadow masks. When theorganic layer 100 is made of a material of a polymer system, we can usepublished ink-jet technology (for example, T. Shimada, et al.:“Multicolor Pixel Patterning of Light-Emitting Polymers by Ink-JetPrinting”, SID 99 DIGEST, 376 (1999)). In this process, the bank 500functions as a torus isolating the picture element area.

A tilted reflective surface 700 is formed on the surface of the slope ofthe bank 500, and is on the transparent electrode 200. The tiltedreflective surface 700 is formed by a high reflective metal such asaluminum, silver or chrome in the process of deposition through masks orin the photolithographic patterning processing. In addition, thefollowing effect can be obtained when the tilted reflective surface ismade of a metal film. In general, the transparent electrode has a higherelectrical resistivity than a metal electrode. Therefore, the displaydevice which has a large display size tends to have the voltagedifference due to the electrical resistivity between the location closeto the power supply and far from it. Due to this voltage difference, theelectric current flowing into the OLEDs including the picture elementdiffers among those close to the power supply and far from it, resultingin the lack of uniformity in the intensity of emitted light. For thisproblem, by forming the tilted reflective electrodes made of a metalthat directly contacts the transparent electrodes, the tilted reflectiveelectrodes works as low resistive electrodes arranged thereon in ameshed formation, and the effect is to suppress the lack of uniformityof emitted light.

For the tilted reflective surface 700, a multiple layered film using atransparent dielectric material such as silicon oxide, silicon nitrideor titanium oxide may be formed for the reflective surface. For thisembodiment, we obtain a feature of loss less reflective surface againstthe light reflection, but drawbacks from a longer manufacturing processand the reflectivity dependence against the wavelength and the tiltangle that are subject to the issues to be studied. In the flat surfacesurrounded by the tilted reflective surface 700, an optical waveguidelayer 600 is formed with a transparent material. The optical waveguidelayer 600 is made of a lower refractive material than that of thetransparent electrode 200. For this embodiment, after a liquid-repellentprocess to the tilted reflective surface 700 corresponding to the spacebetween two picture elements, the optical waveguide layer 600 is formedby a film-forming of the material including a binder resin and a solventby means of spin coating, blade-coating, etc. and finish-processing indry solidification. A selective film-forming using ink-jet printingtechnology for flat surface 25 surrounded by the tilted reflectivesurface 700 can be used before the dry solidification.

In some embodiments, the binder resin that forms the optical waveguidelayer 600 does not have to be self-polymerizing, but includesdry-solidified or polymerize-solidified after film coating. For thislast material, higher durability and tighter contact than that for drysolidification. However, since polymerize-solidification uses UV lightor X ray exposing or thermal heating, a process is selected that doesnot damage the organic layer. For the optical waveguide layer 600, oneof resins or mixed with the plurality of them as transparent acrylicresin, benzocyclobutene resin, polyimide resin, epoxy resin, polyacrylamide resin, polyvinyl alcohol, etc. or photoresist is usable. In someembodiments, the height H2 of the optical waveguide layer 600 is lessthan the height H1 after solidification of the optical waveguide layerfor the previous reason.

On the optical waveguide layer 600, a seal-off material 900 is set bythe gap 950. In some embodiments, the seal-off material 900 includes aglass plate, plastic films which are enhanced for gas-barriercharacteristics using inorganic layers or complex layered material usingthin glass plates and plastic films. The seal-off material can keep agap 950 against the optical waveguide layer 600 with using the bank 500as a spacer and is fixed with the substrate 800 by an adhesive sealmaterial formed around the peripheral of the display portion 2 in a formof a frame. For this fixing, a gap 950 is filled with inert gases suchas nitrogen and the gases are not locked by cementing the seal-offmaterial 900 to the substrate 800 in an air tight manner. In addition,desiccant is put between the seal-off material 900 and the substrate 800as required without degrading the display capability.

Next, we explain the display operation of the display device 1 usingFIG. 8, FIG. 11 and FIG. 12. FIG. 11 is a timing chart of the voltageVG1, VG2, . . . , VGm applied to the gate line G1, G2, . . . , Gm inorder. FIG. 12 shows the voltage status of the gate voltage VG1, thedata voltage VD1 and the voltage of the storage capacitor 23. As shownin FIG. 11, the VG1, VG2, . . . , VGm that turn-on the switchingtransistor 21 are applied to the gate line G1, G2, . . . , Gm in order.When the VG1, which turns on the switching transistor 21, is applied tothe gate line G1 at the time t=t₀, the next turn-on voltage, after onevertical sweep of scanning with one frame term Tf, is applied to thegate line G1 at the time t=t₀+Tf. For this driving scheme, the timeduration to apply the turn-on voltage to the one gate line is less thanTf/m. In some embodiments, the time duration of 1/60 second is used forTf time value.

Once a turn-on voltage is applied to a gate line, all transistors, thatare connected to the gate line transition into a turn-on status andsynchronous data voltages responding to picture signals are applied tothe data lines. This is called a progressive line scanning method.Focusing on the picture element located at the cross point of the firstcolumn and the first row, we explain the gate voltage VG1, the datavoltage VD1 and the voltage status of the storage capacitor 23 withreference to FIG. 12. We assume the value d1 for the data voltage VD1,is synchronous to VG1, and the value d2 for the data voltage at the timeof the next frame t=t₀+Tf. In this embodiment, these data voltages arestored in the storage capacitor 23, while the turn-on voltage is beingapplied to the gate line G1, and these voltages are maintained for oneframe term. These voltages determine the gate voltage of the drivertransistor 22 and the current though the transistor is controlled by thegate voltage. The voltage given by these and common voltage line, andthe voltage Va applied to the transparent electrode determine a electriccurrent which flows into the light-emitting element.

In other words, by synchronously turning-on the voltage applied to thegate lines corresponding to the picture elements of which lightintensity should be controlled, it is possible to control the lightemission of the picture element by applying the voltage corresponding tothe image information through the data lines. Therefore, it is possibleto present a predetermined image by controlling the light emission fromthe plural picture elements that form the display portion 2. Moreover,in some embodiments, the response time of starting light emission afterapplying the voltage between the cathode and anode of the light-emittingelement is less than 1 μs, therefore it is possible to display thepicture image which is a high-speed moving picture. Intense lightemission is generally obtained for bright picture presentation by alarge current that flows through the organic light emitting diode, butelectric power consumption becomes large and the life time of the diode(for example, defined as the life at the half intensity as the initialone) becomes shorter as the current is increased.

As described above, an embodiment can use the light as the image lightwith good efficiency, even though the light is lost during propagationfor the past conventional technology. Therefore, the display devices insome embodiments have more intensity of light, emission and the brighterpicture presentation than those in conventional technologies. In someembodiments, the display device has a lower power consumption thanconventional devices, due to less current flowing into thelight-emitting element and longer life time. Moreover in the displaydevice according to some embodiments, the optical waveguide layer isseparated for each picture element, such that there is no picturedegradation such as optical cross talk or blur of presentation from nolight being guided to other picture elements, resulting in a displaywith clear images and high quality images.

Moreover, we have presented an embodiment where the light emitting areais on the flat plane of the substrate with no step differences due tothe presence of the driving devices or wiring lines thereon, and wherethe step differences due to the driving devices and wiring lines arecovered by the banks; however, the embodiments are not confined to sucha configuration. For example, in some embodiments, on the substrate onwhich the driving devices and the wiring lines are formed, all of thedisplay portion including the step differences due to the driving deviceand wiring lines are covered by a planarizing layer including of aninsulating material, on which a flat surface of those constructingelements such as the reflective electrodes and banks or the like can beformed. In some embodiments, an organic planarizing layer material asacryl base resin, benzocyclobutene resin or polyimide base resin can beused. By the film forming method using spin-coating of these materials,the surface of these films can be flattened. By utilizing the surface onthe wiring lines and driving devices after film formation by planarizingthe layer such as the light emitting area, we can obtain an extensivelight emitting area even though we have less flat area due to the largearea used for wiring lines and driving devices we can realize a brightdisplay device.

In the above embodiment, we have explained the active matrix drivescheme, however some embodiments are not limited to this specificembodiment. For example, we can apply the present embodiment to apassive matrix driving display device, where the electrodes are directlyconnected to the vertical scanning lines and horizontal scanning lines.Moreover, the arrangement of picture elements can be either a stripearrangement, a mosaic arrangement or a delta arrangement, and we canselect an appropriate arrangement to be compliant to the specificationsof the display devices.

Next, we explain the manufacturing method of the first embodimentreferring to FIGS. 13A-13D to FIGS. 16A-16C. FIGS. 13A-13D show aprocess to manufacture the banks in this manufacturing method of thedisplay device. As shown in FIG. 13A, driving devices (such as thin filmtransistors, hereinafter) and wiring lines are formed on the substrate800; and on top of the substrate an insulating layer 890 is formed; andelectrode layer 310, to be used for the reflective electrode 300includes aluminum, magnesium, magnesium-silver alloy, oraluminum-lithium alloy is formed. It should be noted that thin filmtransistors and wiring lines are omitted in the drawings. The electrode310 for the reflective electrode 300 is electrically connected to thethin film transistors for drivers. Next, we coat the photoresist on theelectrode layer 310 for the reflective electrode 300 and make patternsof photoresist by photo-lithography. We etch the electrode layer 310 byusing patterns of photoresist and obtain the island-shaped reflectiveelectrode 300 corresponding to the picture element, as shown in FIG. 13Bafter removing unnecessary photoresist.

Next, we coat a photoresist to a predetermined thickness by spin-coatingthe photoresist on the substrate 800 and on the reflective electrode300. The thickness of the photoresist can be controlled by the viscosityby adjusting the density of the resist since it is solved in a solventand further controlled by the spinning rotation speed of the substratein the film forming process. After coating the photoresist, photoresistfilm 510 is formed by heating and evaporating the solvent. Thephotoresist film 510 is exposed to light through photo masks 810 (FIG.13C), and is developed into the shape of banks 500, located between thepicture elements (as shown in FIG. 13D). There are two kinds ofphotoresists; a negative one and positive one. In some embodiments,since the un-exposed portion is solved in the development for thenegative type resist, the cross sectional shape of the photoresist tendsto be rectangular or close to trapezoid. For the positive type resist,the cross sectional shape of the resist after development is such thatthe side surface of the resist is decreasing in accordance with thelocation of the side surface apart from the surface of the substrate.The selection of positive or negative resist considers the desiredshapes of banks 500 the shapes closer to the desired ones are obtained.

In some embodiments, the negative type resist, includes a cinnamic acidbase resist or rubber base resist as cyclized rubber added with bisazidecompound for photosensitive radical. In some embodiments, the positivetype resist includes a mixed material of naphtoquinonediazido compoundfor photosensitive agent and alkali-soluble phenolic resin. An exampleof the positive type resist, there is a commercial product call “OPTOMERPC” (manufactured by JSR Corporation). This resist is a mixture of acrylbase resin and naphtoquinonediazido compound. In some embodiments, theviscosity is, for example for the use of “OPTOMER PC403”, controlled fora 3.5 μm thick film formation when coated at a spinning speed of 700rpm.

For this embodiment, we coat the photoresist on the substrate, dry bythermal heat and photo-expose by using a photo mask so that the areas ofthe banks are exposed. By these processes (as exposure, development andheating), we obtain the bank 500 in a cross sectional shape as shown inFIG. 14. The tilt angle β of the side surfaces of the bank closest tothe substrate surface ranges from 30° to 60° depending upon the processcondition, and continuously decreases according to being apart from thesubstrate surface. For example, we obtain an angle β of about 60° andthe tilt angle is 20° for a height of 3 μm for the bank that has a 3.5μm height. This bank can be used for this embodiment. In someembodiments, we use photosensitive polyimide as a positive typephotoresist product of which code is HD8010XF2 (Hitachi Chemical Co.Ltd.).

As for the photo mask 810, in some embodiments, we use ultra-violetlight-transmissive fused silica substrate on which shadow pattern isformed by the metal film. In some embodiments, we use a photo mask thathas light control capability by controlling the thickness of the shadowmetal or the area of the plural small open hole at the location of theshadow masks that are effective to the transparency change in acontinuous, manner. In some embodiments, we discussed the process to usephotoresist for making the banks because we can manufacture the banks ofseveral micron meters height in a shorter processing time.

However, in some embodiments, we use an inorganic material such assilicon oxide or silicon nitride for the use of banks. For theembodiment of using silicon nitride, we can form the bank by the siliconnitride layer formed by CVD (Chemical Vapor Deposition) on thesubstrate, and pattern by etching through the resist pattern andremoving the unnecessary photoresist thereon. By varying the densityconditions of the NH3 and SiH4 supplied for the film forming process, wecan control the shape of the tilted surface of the bank after etchingdue to multiple layers of silicon nitride with different filmproperties. Any forming method, for example a screen printing method ordirect drawing of the ink-jet, is used to form the bank 500 as long asthe required tiled surfaces are obtained.

FIGS. 15A-15C show the process to manufacture the organic layer portionof the display device according to an embodiment. We make the bank 500in the previously described process, and then we form the organic layer100 on part of the tilted surface of the bank 500 and on the reflectiveelectrode 300 in the area surrounded by the bank 500. As shown in FIG.15A, the forming of the organic layer 100 is performed by depositing theorganic material via a metal mask which has open areas corresponding tothe locations of the light emitting areas. For this embodiment, the bankcan be used as a spacer to suspend the mask. For the embodiment when theorganic layer is a polymer type, the film forming is performed byblowing the solution of solvent and the organic material from theink-jet head 830 using the control method with a piezo device, asso-called ink-jet patterning technology as shown in FIG. 15B. For thismethod, the banks 500 can function as dams to store the ink-droplet.

After forming the organic layer, the transparent electrode 200 is formedon all of the display portions. In some embodiments, the transparentelectrode includes electrically conductive transparent film such as ITOor IZO, and is formed by vacuum evaporation or sputtering process (seeFIG. 15C). However, it is difficult to form low resistive transparentfilm by using the conventional deposition method and damage to theorganic layer 100 result in the degradation of the characteristics ofthe embodiment described using sputtering method. Therefore, an ionplating device or a counter target sputtering device, where plasma doesnot directly contact the surface of the substrate, is better to be usedin forming the transparent electrode 200 in order to minimize damage. Wecan form a thin metal deposition film through which the light transmitsdirectly onto the organic layer before forming the transparentconductive film. We may exploit the transparent conductive filmdeposited on this thin metal deposition film for the transparentelectrode. For this embodiment, the thin metal deposition film functionsas a blocking layer, such that it is possible to reduce the damage ofthe organic layer. In some embodiments, the blocking layer, includes ametal such as gold, platinum or chrome that has a high work function anda thickness of about 10 nm.

FIGS. 16A-16C show the process to manufacture the optical waveguidelayer of the display device according to an embodiment. As shown in FIG.16A, we form the tilted reflective surface 700 by selectively depositinga high reflective metal such as aluminum using a metal mask that hasopen holes corresponding to the banks 500 made in the process describedabove. Afterwards, we blow the compound material for the opticalwaveguide layer to the basin area surrounded by the bank 500 through theink-jet head 850 as shown in FIG. 16B. The compound material includessolvent and the binder resin is transparent for visible light. We formthe optical waveguide layer 600 which is slightly lower than the top endof the tilted reflective surface as shown in FIG. 16C in such a way thatthe compound material of the optical waveguide layer is stacked up tothe height of the bank or slightly lower than that of the bank, is keptfor a mean time enough to get wet with the transparent electrode 200 andthe tilted reflective surface 700 and to obtain leveling and then dryand solidify. We may form the predetermined optical waveguide layer byrepeatedly blowing the compound material for the optical waveguidelayer, dry and solidify.

For the binder resin of the optical waveguide layer 600, in someembodiments, the binder resin has no polymerization property, but ismerely dried for solidification and another binder resin that issolidified by a polymerizing process after film formation. The resinthat can be solidified by polymerizing process has tighter contact andhigher durability than the simple dry and hardening process, however,the exposing to ultraviolet light or electron beam or heating are variedin order to obtain the least damage to the organic layer.

We can use a resin or a complex mixture of resins from acrylic resin,benzocyclobutene resin, polyimide resin, epoxy resin, polyacryl amideresin, polyvinyl alcohol, etc. By using such material for the opticalwaveguide layer 600, it is possible to make an optical waveguide layerthat has smaller refractive index than such transparent electrodes asITO and IZO and larger one than the air.

As for forming the optical waveguide layer, the film forming of theoptical waveguide layer compound material is performed by coating thesubstrate using a spin-coater drying for hardening besides selectivelydepositing the compound in the area of the basin surrounded by the banksby using ink-jet. In this embodiment, the substrate is exposed to O2plasma and then CF4 plasma after forming the tilted reflective surface,but before forming the layer of the optical waveguide layer compoundmaterial. In this embodiment, the tilted reflective surface made ofaluminum which is only fluorinated has liquid-repellency, and thetransparent electrode which is not fluorinated, maintains wettablesurface characteristics to the optical waveguide layer compoundmaterial. Therefore, the optical waveguide layer compound material stayson the area to which the transparent electrode surface is exposed, andnot on the tilted reflective surface. This results in the opticalwaveguide layers isolated by the tilted reflective surface for each ofthe picture element.

In some embodiments, it is desirable that the optical waveguide layer iscompletely isolated by the tilted reflective surface, however, each ofthe isolated waveguide layer it connects to that on the adjacent pictureelement beyond the tilted reflective surface. For this embodiment, inthe area where the optical waveguide layer is thinnest, mostly at theridgeline of the bank, the thickness of the optical waveguide layer isless than the visible light wavelength and waveguide modes are solimited that only a little amount of light leaks to the next pictureelement. Therefore, even though the optical waveguide layer hascontinuity to adjacent picture elements, the optical waveguide layer ispractically isolated provided the thinnest optical waveguide layer isless than the visible light wave length. Therefore this embodiment doesnot necessarily exclude such continuity of the optical waveguide layer.

As shown in FIG. 1, the seal-off material is fixed with the substrate800 by adhesive sealing cement formed in a frame shape around theperipheral area of the display portion by keeping the gap 950 betweenthe seal-off material 900 and the optical waveguide layer 600 with thebank 500 as a spacer. The gap 950 has an equivalent refractive index ofair by filling the inert gas as nitrogen with the gap 950 between theseal-off material 900 and the substrate 800. As for the seal-offmaterial 900, we can use a transparent (for visible light), gas-barriercapable plates such as a glass plate, a plastic film processed for gasbarrier, a multi-layer with glass plates and the plastic films.

The Second Embodiment

Next, we will explain another embodiment of the display device. FIG. 17shows a cross sectional view of another embodiment of the displaydevice. In this display device, the height H3 of the optical waveguidelayer located at the central area of the basin area surrounded by thebank 500 is continuously larger as being closer to the bank 500. Besidesthe height H4 of the optical waveguide layer 600 on the tiltedreflective surface 700 is larger than H3, we will use the same signs andnotations for the same portions and omit the detailed explanation.

For the optical waveguide layer 600 which satisfies the relation ofthese heights, we can form it by controlling the dry out speed of thecoated optical waveguide layer compound material when we coat theoptical waveguide layer compound formed of binder resin and solvent withtaking the boiling point and the vapor pressure of the solvent in theroom temperature into account. In other words, we can obtain the opticalwaveguide layer in a form that the height is low in the central areasurrounded by the bank and is high on the tilted reflective surface 700,in accordance with the volume shrinkage after coating the opticalwaveguide layer compound, leveling the coated film and drying forsolvent evaporation. In this embodiment, the surface of the opticalwaveguide layer 600 is not parallel, but declines to the surface of thesubstrate.

Next, we will explain the effect of the optical waveguide layer 600described above. FIG. 18 and FIG. 19 show embodiments where the opticalwaveguide layer 600 has a different height for each location, that is,the surface of the optical waveguide layer 600 is not parallel to thesubstrate. FIG. 18 shows the embodiment where the height of the opticalwaveguide layer on the upper location of the light 2100 which isemitting the light at location 190 is lower than the height of the layerat the location 690 where the light 2100 reflects on the surface of theoptical waveguide layer. We assume the incident angle and reflectionangle of the light 2100 at the surface of the optical waveguide layeragainst the surface parallel to the substrate as θ3 and θ4,respectively. Then the relation θ3>θ4 is satisfied, the light reflectedon the surface of the optical waveguide layer is more parallel to thesubstrate. Therefore, the times of reflecting on the reflectiveelectrode 300 until the light traveling until reaching to the tiltedreflective surface in the optical waveguide layer decrease, and thelight loss by absorbing the light at the reflective electrode, resultsin improving the external coupling efficiency.

On the other hand, FIG. 19 shows the case where the height of theoptical waveguide layer on the upper location of the light 2100 which isemitting the light at location 190 is higher than the height of thelayer at the location 690, where the light 2100 reflects on the surfaceof the optical waveguide layer. We assume the incident angle andreflection angle of the light 2100 which is totally reflected at thesurface of the optical waveguide layer against the surface parallel tothe substrate as 83 and 84, respectively. Then the relation θ3<θ4 issatisfied, the light reflected on the surface of the optical waveguidelayer is more vertical to the substrate. Therefore, the totallyreflected light on the optical waveguide layer surface at the first timehas the smaller incident angle when the light again incidents thesurface of the optical waveguide layer. If the incident angle is smallerthan the critical angle, then the light comes out to an outer viewerbefore the light comes up to the tilted reflective surface. Thereforewhen the outer surface of the optical waveguide layer tilts to thesubstrate, higher external coupling efficiency is obtained than in thecase where the optical waveguide layer is parallel to the substrate.

The Third Embodiment

Next, we will further explain another embodiment of the display device.FIG. 20 shows a cross sectional view of a picture element in anotherembodiment. For this embodiment of the display device, the thickness ofthe optical waveguide layer has the maximum at the center of the areasurrounded by the bank 500 and is continuously decreases the closer tothe bank. Since the fundamental construction is same as the embodimentdescribed above other than the shape of the optical waveguide layerbeing convex, we mark with the same signs and notations to the sameportions and avoid the explanation. This shape of the optical waveguidelayer is made by making the tilted reflective surface 700liquid-repellent and the transparent electrode 200 exposed to theoptical waveguide layer liquid-wettable before coating the opticalwaveguide layer compound material formed of binder resin and solvent. Asa concrete process, the substrate is exposed to oxygen plasma and CF4plasma in order before coating the optical waveguide layer compoundmaterial.

In this embodiment, if the tilted reflective surface is made of aluminumthen the surface is fluorinated and has liquid (water)-repellentcharacteristics, however the transparent electrode is not fluorinatedand keeps wettable surface characteristics against the optical waveguidelayer compound material. Instead of these processes, we can make thetilted reflective surface liquid-repellent and the transparent electrodeexposed to the optical waveguide layer selectively liquid-wettable bycoating all over the substrate with a transparent wettability-convertedlayer which is not shown in the figures. The wettability-converted layercan be formed by coating a solution in which the binder resin, thephotocatalyst and the necessary additives are dispersed, drying andfixing the photocatalyst in the hardened resin. If the thickness of thewettability-converted layer is large, then it allows guiding the lightand causes the optical cross-talk by light leak to other pictureelements. Therefore, in some embodiments, the particle size of thephotocatalyst should be less than 10 nm and the layer being less than300 nm. In some embodiments, we use titanium oxide for the photocatalystand organosiloxane polymer for the binder resin. After forming thewettability-converted layer and photo-exposing with the tiltedreflective surface blocked off from the exposure, and the transparentelectrode exposing to the optical waveguide layer through the photomask, the exposed wettability-converted layer changes to be highliquid-wettability and the non-exposed one maintains to beliquid-repellent.

After making the tilted reflective surface 700 liquid-repellent and thetransparent electrode 200 exposed to the optical waveguide layerliquid-wettability, the coated optical waveguide layer compound materialturns into a convex shaped optical waveguide layer such that thethickness of the optical waveguide layer is the maximum at the center ofthe area surrounded by the bank and continuously decreases towards thebank 500. For this construction, improvement of the external couplingefficiency can be expected due to the slope of the optical waveguidelayer 600 against the substrate surface.

The Fourth Embodiment

Next, we further explain another embodiment of the display device. FIG.21 shows the cross sectional view of a picture element that explainsanother embodiment. This embodiment has an increased optical waveguidelayer and the maximum height of the layer is higher than the height ofthe bank; therefore, the fundamental construction is same as theembodiment described above. From this reason, we use the same signs andnotations for the same portions and omit detailed explanations. In thisembodiment, it is possible to make the ridgeline of the bankliquid-repellent and the other parts including the tilted reflectivesurfaces selectively high liquid-wettable by blocking the light exposureonto the ridgeline of the bank when the light is exposed to thewettability-converted layer. In this embodiment, improvement of theexternal coupling efficiency can be expected due to the slope of theoptical waveguide layer 600 against the substrate surface. In addition,a display device that has high intensity of the light emission normal tothe front surface is realized due to the focusing effect of the opticalwaveguide layer as the convex surface shape of the optical waveguidelayer. However, in some embodiments, the bank 500 is not used as aspacer between the substrate 800 and seal-off material when they aretightly cemented. Therefore, in some embodiments, we use an adhesiveseal material including beads or small rods pasted at the peripheralarea of the display portion in a shape of a frame to such area and thenthe substrate 800 and the seal-off material 900 are fixed in nitrogengas filled therebetween.

The Fifth Embodiment

Next, we explain another embodiment of the display device. FIG. 22 showsa cross sectional view of the picture element of the display device.This embodiment is a modification of the embodiment explained in FIG. 1such that the seal-off material 900 is replaced by an optical waveguidelayer 650 (called a gas-barriering optical waveguide layer, hereinafter)that is transparent and high density and has a high gas-barriercharacteristic and that is further formed on the optical waveguide layer600. Since the other constructions are the same as the above embodiment,we use the same signs and notations for the same portions and omitdetailed explanations. For the gas-barriering optical waveguide layer,we can use silicon nitride, titanium oxide and we optimize the conditionsuch as the gas flow rate when using chemical vapor deposition method bywhich we form a dense film. We form a multi-layered gas-barrier layerinstead of a single layer, and moreover we optically isolate the layeron each of the picture elements by using photo-lithography technology(when needed). Being same as the above embodiment, the external couplingefficiency is improved and the display device that presents a distinctpicture quality and has no optical cross talk, is realized. Especially,there is a merit that a thin and light display device is realized sinceno seal-off material is used.

The Sixth Embodiment

Next, we explain another embodiment of the display device. FIG. 23 showsa cross sectional view of the picture element of the display device.This embodiment modifies the embodiment explained in FIG. 1 such that atilted reflective surface 700, which has a reflective electrode, isformed on the reflective electrode 300 and the slope surface of the bank500 before forming the organic layer 100 and the organic layer 100,transparent electrode 200 and the optical waveguide layer 600 are formedthereon. Since the other constructions are same as the above embodiment,we use the same signs and notations for the same portions and omitdetailed explanations. We explain the fabrication process of theembodiment shown in FIG. 23 in referring to FIGS. 24A-24C, FIGS. 25A-25Cand the drawing of the previous embodiment. FIGS. 24A-24C and FIGS.25A-25C are process drawings that explain the manufacturing method ofanother embodiment shown FIG. 23.

The process for this embodiment is same as the previous embodiment up tothe step where driver elements and wiring lines are formed, and theisland-shaped reflective electrode 300 including aluminum, magnesium,magnesium-silver alloy or aluminum-lithium alloy and banks 500, thatcorrespond to the picture element, are constructed on a substrate 800with an insulating layer 890 on the upper surface. In the next step, weform a layer of a reflective metal material similar to the reflectiveelectrode 300 over all surfaces of the display portion, and then weconstruct the island-shaped tilted reflective surface 700, thatcorresponds to the picture element, on the reflective electrode 300 andthe slope surface of the bank 500 by applying photolithographytechnology and etching as shown in FIG. 24A. Therefore, the tiltedreflective surface 700 and the reflective electrode 300 are electricallyconnected and then the tilted reflective surface 700 functions as areflective electrode.

In the next step, similar to the above embodiment explained by usingFIGS. 15A-15C, the organic layer 100 is formed by selective depositionthrough masks or selective ink-jet patterning. In this embodiment, theorganic layer 100 is formed in an extensive area so that it completelycovers the edges of the tilted reflective surface 700 (as shown in FIG.24B). Because a failure is caused by the electrical short between thetilted reflective surface and the transparent electrode 200 formed onthe organic layer 100 if the edge of the tilted reflective surface isunconcealed.

In the next step, the transparent electrode 200 is formed all over thedisplay portion as shown in FIG. 24C. In some embodiments, we use ITO orIZO for the transparent electrode as described in the above embodimentand we form it in the same method used for such embodiment. As furthershown in FIG. 25A, we coat the wettability-converted layer over thedisplay portion. The wettability-converted layer is the layer for whichwe can change the wettability of a selectively predetermined area asliquid-repellant to liquid-wettable or vis-a-vis. We can use a filmconsisting of a photocatalyst and a binder resin. For this embodiment,the wettability-converted layer can be formed by coating a solution inwhich the binder resin, the photocatalyst and the necessary additivesare dispersed on solvent, drying and fixing the photocatalyst in thehardened resin. If the thickness of the wettability-converted layer islarge, then it allows guiding the light and causes the opticalcross-talk by light leakage to other picture elements. Therefore, insome embodiments, the particle size of the photocatalyst should be lessthan 10 nm and the layer is less than 300 nm. In some embodiments, wecan exploit titanium oxide for the photocatalyst and organosiloxanepolymer for the binder resin. After forming the wettability-convertedlayer and photo-exposing through a photo mask 870, the exposedwettability-converted layer turns to be high liquid-wettability and thenon-exposed one maintains to be liquid-repellent.

Therefore, the ridgeline of the bank 500 corresponding to the isolationgap between the picture elements maintain liquid-repellency, and theother portion changes to be highly liquid-wettable after light-exposingto the wettability-converted layer through a photo mask 870 which blocksthe light for the ridgeline of the bank 500 corresponding to such anisolation gap and lets the light transmitting to other portions (asshown in FIG. 25B). In the next step, the optical waveguide layercompound material 680 is blown onto the basin area surrounded by thebank 500 from the ink-jet head 880 as shown in FIG. 25C. For at leastthe same reasons explained in reference to the embodiment of FIG. 16,the optical waveguide layer compound material at least includes solventand binder resin which is transparent to the visible light. The opticalwaveguide layer compound material is stacked up to the level similar tothe height of the tilted reflective surface 700. In this embodiment, theblown optical waveguide layer does not stay on the ridgeline of the bank500 and moves to a puddle in the basin area surrounded by the bank 500.After we keep the blown optical waveguide layer compound material toobtain enough leveling, we then form the optical waveguide layer 600which is optically isolated on each picture element by making the levellower than the upper edge of the tilted reflective surface 700 after dryand solidification. In addition, we can form the construction of theoptical waveguide layer not only by a single process of blowing theoptical waveguide layer compound material, drying and solidifying, butby repeating such process.

As the next step, we fix the seal-off material 900 with the substrate800 by an adhesive seal material formed around the peripheral of thedisplay portion in a form of a frame in a status that a gap 950 betweenseal-off material 900 and the optical waveguide layer 600 is kept by thebank 500 as a spacer. The gap 950 has an equivalent refractive index ofby filling the inert gas as nitrogen between the seal-off material 900and the substrate 800. In this embodiment and the above embodiments,being different from the conventional technology where the lightpropagates in parallel to the substrate, and then is attenuated, thelight is guided by the optical waveguide layer 600 to the tiltedreflective surface 700, and then changes direction of propagation by thereflection at the tilted reflective surface 700, and is used as aneffective display image light to the viewer resulting in the improvementof the external coupling efficiency. Since the optical waveguide layer600 is completely isolated, the light emitted from an organic layer of acertain picture element does not propagate in other different pictureelements and no picture quality problem such as optical cross-talk orblur of presentation occurs, thus resulting in a display device that hasa high quality picture image. Moreover, in this embodiment, the tiltedreflective surface 700 does not only function as a reflection surface,but also as a reflective electrode of OLED including the reflectionelectrode, the organic layer 100 and transparent electrode 200.Therefore, the slope surface of bank 500 is used for the emission areaas well as the flat surface 25, therefore, when the relatively extensiveemission area in comparison to the embodiment shown in FIG. 1 is used, abrighter display device is obtained on the basis of the same size ofpicture element.

FIG. 26 shows a cross-sectional view of the display device of anembodiment. The reflective electrode 300 electrically connects with thedriver element on the area covered by the bank 500 similar to the aboveembodiment. In other words, the electrode 26 of the driver transistorand the reflective electrode 300 are connected through the contact hole31 in the insulation layer 30. The contact hole 31 is located underneaththe bank 500 and the tilted reflective surface 700. Thus, the contacthole area which is not used as a light emitting one is located under thetilted reflective surface, and the other area that emits the light isthe light emitting area. This construction is efficient for realizinghighly intense light emission.

The Seventh Embodiment

Next, we explain another embodiment. FIG. 27 shows a planar view of thedisplay device of an embodiment. A unit picture element is shown as oneof additive primary colors given by a red-color emission pixel, agreen-color emission one and blue-color emission one therein. The pixelin this embodiment is constructed as picture element 20 of the displaydevice explained in FIG. 1, and FIG. 2 is separated by the tiltedreflective surface 700 and the bank 500 into a plurality of areas foreach of such pixel. Since the other constructions are the same as aboveembodiment, we use the same signs and notations for the same portionsand omit detailed explanations.

In the display device for this embodiment, a picture element isseparated into a plurality of light emitting areas and we can controlthe viewing angle characteristics of the device by changing the relationbetween the size of the area and the height of the optical waveguidelayer 600. This is, as described above, from the fact that the height ofthe tilted reflective surface and the thickness of the optical waveguidelayer 600 (against the size of the light emitting area) influence theexternal coupling efficiency. In other words, the longer the width ofthe light emitting area against a certain height of the tiltedreflective surface and a certain thickness of the optical waveguidelayer is formed, then the smaller the external coupling efficiency; andconversely the shorter the width of the light emitting area, the largerthe external coupling efficiency and the wider viewing angle areobtained. For the above embodiment explained in referring to FIG. 2, theviewing angle for the horizontal orientation is larger than that of thevertical orientation against the drawing plane. On the other hand, thedisplay device that has the same viewing angle characteristics forvertical orientation and horizontal orientation is realized bysegregating the light emitting area of a picture element into aplurality of light emitting areas, and making the length H3 in thevertical orientation the same as the length W2 in the horizontalorientation. In some embodiments, the external coupling efficiency canbe larger, regardless of the size of the picture elements, than that inthe case of using non-segregated picture element by segregating thepicture element into a plurality of light emitting areas since we canshorten the width of the light emitting area against the height of thetilted reflective surface and the thickness of the optical waveguidelayer. Therefore, a brighter display device is realized in comparison toother ones which consume the same electric power.

FIG. 28 shows the cutaway view along line C-C of an embodiment shown inFIG. 27. A picture element in this embodiment is segregated into aplurality of areas by the bank 500 as described above. In order tosuppress the increase of the fraction due to the increase of thequantity of the driver elements, these segregated areas corresponding toa picture element are driven by a pair of driver elements of whichconfiguration does not complicate the circuitry. For this purpose, thereflective electrode 20 is not segregated and a single island-shapedreflective electrode 300 is made for a single picture element 20.Therefore, the bank 500 that segregates the picture element into aplurality of areas is formed on the reflective surface 300 as shown inFIG. 28. For this embodiment, since the reflective electrode 300connects to other portions of the electrode on the flat surface underthe bank 500, therefore no failure due to the break by the stepdifference occurs. Moreover, the transparent electrode 200 is hard to bebroken at the ridge of the bank 500 since the tilted reflective surface700 that functions as an electrode is stacked on the transparentelectrode.

FIG. 29 shows the cutaway view along line C-C for an embodiment shown inFIG. 27 for the embodiment shown in FIG. 23. For this embodiment, thereflective electrode is not segregated, a single island-shapedreflective electrode 300 is made for a single picture element 20 and thebank 500 that segregates the picture element into a plurality of areasis formed on the reflective electrode 300 as shown in FIG. 29. Thereforeno breaking of electrode occurs due to the step difference by the bank500 since the reflective electrode 300 connects other portions of theelectrodes on the flat surface. Moreover, the shape of the pixelssegregated from a picture element can be any one as a polygon as atriangle and a hexagon, an ellipsoid or a circle as far as we can obtainthe desired viewing angle characteristics.

The Eighth Embodiment

Next, we will explain another embodiment. FIG. 30 shows a crosssectional view of a picture element explaining another embodiment of thedisplay device. This embodiment is the display device where amodification is applied to the embodiment explained in FIG. 23 such thatthe reflective electrode is eliminated, and the tilted reflectivesurface 700 shown in FIG. 23 is replaced by the reflective electrode 350that functions as the tilted reflective surface 700 shown in FIG. 30 aswell. Since the other constructions are the same as the aboveembodiment, we use the same signs and notations for the same portionsand omit detailed explanations. For this embodiment, a quantity offabrication process reduces and the productivity is improved by highthroughput because the reflective electrode and the tilted reflectivesurface are formed by a single layer. However, for this construction,there is a possibility of failure as no light emitted from a part of apicture element because the reflective electrode 350 tends to be brokenon the ridge of the bank 500 if the picture element is segregated into aplurality of light emitting areas.

FIG. 31 shows a planar view showing a part of the display device of anembodiment. It shows a unit picture element formed of one of additiveprimary colors given by a red-color emission pixel, a green-coloremission one and blue-color emission one therein. In this embodiment, aportion of the bank 500 that segregates the picture element into aplurality of areas as shown in the above embodiments is eliminated sothat the areas are combined into a single flat surface. Therefore, thepicture element is formed into a flat surface of which portions arelinked by flat surface 550 which is the surface on which no bank portionexists. In other words, the reflective electrode, the organic layer andthe transparent electrode are formed in a single flat plane withoutriding over the step difference caused by the bank. Therefore, asexplained in the above embodiment by using FIG. 30, the connection ofthe electrode is maintained by the flat plane area even for theconstruction that the electrode may be cut on the ridgeline of the bankand the failure such that no light emits from a part of area of thepicture element does not occur. In other words, the failure of theelectrode break is prevented by eliminating a portion of the bank tomake a single combined flat plan in the picture element.

The Ninth Embodiment

Next, we explain another embodiment. FIG. 32 shows a cross sectionalview of a picture element explaining another embodiment of the displaydevice. This embodiment is the display device where a modification isapplied to the embodiment explained in FIG. 1 such that the organiclayer that is divided into a red-color pixel, green-color one and ablue-color one is made a single blue-color organic layer, and theoptical waveguide layer on the area of the red-color pixel and that ofthe green-color pixel have color changing medium layers such asred-color fluorescence and green-color fluorescence are generated by theillumination of the blue-color light emission from the single blue-colororganic layer, respectively. Since the other constructions are same asthe above embodiment, we use the same signs and notations for the sameportions and omit detailed explanations. Several methods for full colorOLED display have already been proposed, and proven several methods forfull color OLED display, among which there is a technical method ofcombining blue light-emitting element and fluorescent color changingmedia (called CCM method, hereinafter). The CCM method is to excite thefluorescent dye layer by blue light emitting from blue light emittinglayer and obtain the green light and the red light converted thereby,resulting to make three primary color lights. (see The journal of theinstitute of image information and television engineers, Vol. 54, No. 8,pp. 1115-1120).

Next, we explain another embodiment by applying the CCM method. Thepicture element that emits blue light is formed, as same as the aboveembodiment, with a single optical waveguide layer, however the pictureelements which emit red and green lights are formed with the firstoptical waveguide layer 601, the color changing medium layer 602 and thesecond optical waveguide layer 603 stacked in this order in the basinarea surrounded by the bank 500.

The first and the second optical waveguide layers include transparentresin or transparent inorganic material such as silicon nitride, siliconoxide, titanium oxide, etc. In some embodiments, the refractive index ofthe first optical waveguide layer 601 is larger than that of thetransparent electrode 200. Because the light emitted from the organiclayer 100 that penetrates the transparent electrode 200 is not totallyreflected at the boundary surface between the first optical waveguidelayer 601 and the transparent electrode 200, is led into the colorchanging medium layer 602 with high efficiency, we can obtain a largeexternal coupling efficiency by the large amount of the desired lightconverted in the color changing medium layer. In some embodiments, wecan use titanium oxide as the higher refractive optical waveguide layermaterial than ITO or IZO.

In some embodiments, it is important that the heights of the colorchanging medium layer and the second optical waveguide layer are lowerthan that of the tilted reflective surface. In this embodiment, thelight of the light emitted from the color changing medium layerpropagates in the optical waveguide layer when it is emitted almostparallel to the surface of the optical waveguide layer, and then someportion of the light is reflected on the tilted reflective surface andgoes towards the viewer 1000 as an image picture light. This reflectionraises the external coupling efficiency. We can prevent the opticalcross-talk and blur since the light emitting from the color changingmedium 602 does not travel into other picture elements and no lighttravels through the other picture elements and reaches the viewer 1000after the reflection at the tilted reflective surface surrounding theother picture elements. Therefore, we can obtain clear images andpictures and a high quality picture is realized. Though we can obtain animprovement of the external coupling efficiency without the secondoptical waveguide layer 603, in some embodiments, a gap 950 has asimilar refractive index of air between the color changing medium layerand seal-off material. Because in embodiments of no gap, the light ofthe light emitted from the color changing medium layer partly travelsinto the seal-off material and is lost therein, or partly propagatesinto other picture element and comes to the viewer 1000 which results inthe optical cross-talk and blur.

Next, we explain another embodiment. The embodiment is a modificationapplied to the above embodiments explained by referring to FIG. 1 andFIG. 2 such that the organic layer that is separately designed for ared-color light emitting picture element, green-color light emitting oneand blue-color light emitting one are used for a white-color lightemitting form the organic layer, the red-pigment, green-one and blue-oneare mixed and dispersed in the optical waveguide layers corresponding tothe red-color, the green-color and the blue-color lights emittingpicture elements, respectively. Since the other constructions are sameas the above embodiment, we omit detailed explanations for the portionthat has the same function.

There are two kinds of the constructions; the organic layer that emitswhite-color light as stacked layers of which each layer has differentlight emission for each other and a single layer that includes differentdoped dies that emit different color lights. An example for the formeris a combination of TPD and partly doped Alq3 with Nail red and1,2,4-triazole derivative (TAZ). An example for the latter is doped PVKwith three kinds of dopants, for example 15 1,1,4,4-tetraphenyl-1,3butadiene, coumarin 6, DCM1. In some embodiments, for either material,the white-color light emitting organic layer has high emissionefficiency and long life.

The optical waveguide layer is, as same as the embodiment explained byreferring to the FIG. 16B, formed by blowing the optical waveguide layercompound material from the ink-jet head 850 to the basin area surroundedby the bank 500. In this embodiment, the optical, waveguide layercompound includes pigment other than solvent and transparent binderresin. As for the pigments included in the optical waveguide layer whichis formed with the optical waveguide layer compound blown are mixed anddispersed for each picture elements as red, green and blue pigments forthe picture elements for red-, green- and blue-colors, respectively. Wecan exploit those pigments used for the color filters applied to liquidcrystal display devices.

In this embodiment, the white-color light emitted from the organiclayer, directly or after reflecting on the reflective electrode, travelsinto the optical waveguide layer and the light of the wave-length whichis different from the spectrum of the color of the included pigmentfilters is mostly absorbed, though, for example, the light which has thewavelength corresponding to the red-color light can penetrate theoptical waveguide layer which corresponds to the red-color pictureelement due to inclusion of such pigment. Therefore, the light thattravels to the viewer after penetrating the optical waveguide layer ortraveling in the optical waveguide layer, and then reflecting on thetilted reflective surface is the red light provided it emits from thepicture element designed for the red-color light emission. Similar tothe red color picture element for the picture element designed forgreen-color or blue-color light emission, we can obtain the lights ofthese colors. For this embodiment, we need one organic layer, theprocess features to be easy fabrication since no coloring from suchthree primary colors for each picture element. In addition, in someembodiments, similar to the above embodiments, we can improve theexternal coupling efficiency by the effects of the optical waveguidelayers and the tilted reflective surface and obtain high quality imagewhich has no optical cross talk and does the clear image.

In the embodiments we have discussed, we have shown so-called activematrix type display devices such as the presentation of the image isperformed by controlling the operation of a plurality of light-emittingdiodes that form a plurality of picture elements aligned in a formationof matrix with the use of driver elements, however, this embodiment isnot confined to such embodiments. In other words, the construction thathas improved the external coupling efficiency shown in the aboveembodiment can be applied to so-called passive matrix type displaydevices and to merely illuminating devices. As for the light emittingelements, the device that light-emits in the medium which has largerrefractive index than air, and that has a flat plan in at least a partof the light emitting layer, such as inorganic electro-luminescentdevices or inorganic light emitting diodes, can be applied to one ormore embodiments of this disclosure.

The invention claimed is:
 1. A display device including a plurality of light-emitting elements aligned on a TFT substrate in a formation of a matrix, wherein the display device comprises: the plurality of light-emitting elements each having a flat surface portion and including a light-emitting layer, an anode, and a cathode; an insulating layer formed on the TFT substrate and under the light emitting element; and a tilted metal surface is provided on a peripheral area surrounding the flat surface portion of the light-emitting element and has a tilt angle with respect to the flat surface portion of the light-emitting element; wherein the tilted metal surface is provided on a surface of a slope of a bank that is provided on the insulation layer; wherein a width of a cross-section of the bank becomes smaller as the cross section comes farther away from a surface of the TFT substrate; wherein a counter substrate is placed on the TFT substrate; and wherein a gap exists between the light emitting element and the counter substrate.
 2. The display device according to claim 1, wherein the display device comprising a plurality of pixels aligned on the TFT substrate in a formation of a matrix; and wherein each of the plurality of pixels includes one of the plurality of light-emitting elements.
 3. The display device according to claim 1, wherein an optical waveguide layer is overlaid in an area surrounded by the tilted metal surface on the light emitting element.
 4. The display device according to claim 3, wherein the optical waveguide layer has a cross sectional formation so that a cross sectional width of the optical waveguide layer becomes wider as a distance from the surface of the TFT substrate increases; and wherein a height of the tilted metal surface from the flat surface of the light-emitting layer is larger than a maximum height of the optical waveguide layer.
 5. The display device according to claim 1, wherein inactive gas is arranged in the gap.
 6. The display device according to claim 1, wherein the bank is sandwiched between the tilted metal surface and the anode in the peripheral area surrounding the flat surface portion of the light-emitting element; and wherein the bank is not arranged on the flat surface portion of the light-emitting element in plan view.
 7. The display device according to claim 6, further comprising: a plurality of driver elements each connected to each of the light-emitting elements; a plurality of capacitor elements each of which is connected to one of the light emitting elements and receives one of a plurality of image signals; and a plurality of switching elements each of which is connected to one of the capacitor elements and one of the light emitting elements and controls input of one of the plurality of image signals to one of the capacitor elements; wherein the insulating layer has a contact hole formed on the driver element; wherein the anode is formed on the insulation layer and is connected to the driver element via the contact hole; wherein the bank is formed to cover the contact hole.
 8. A display device including a plurality of light-emitting elements having a flat surface portion and including an organic layer, an anode and a cathode; an insulating layer formed on the TFT substrate and under the light emitting element; a first metal surface is provided on a surface of a slope of a first bank that is provided on the insulation layer; a second metal surface is provided on a surface of a slope of a second bank that is provided on the insulation layer; wherein the flat surface portion of the light-emitting element is arranged between the first metal surface and the second metal surface; wherein a width of a cross section of each of the first and the second banks becomes smaller as the cross section comes farther away from a surface of the TFT substrate; wherein a counter substrate is placed on the TFT substrate; and wherein a gap exist between the light emitting element and the counter substrate.
 9. The display device according to claim 8, wherein the anode, the organic layer including a light-emitting layer, and the cathode is arranged in this order; wherein at the flat surface portion of the light-emitting element, the anode is connected to the organic layer, and the organic layer is connected to the cathode.
 10. The display device according to claim 9, wherein an optical waveguide layer is overlaid on the flat surface portion of the light-emitting element.
 11. The display device according to claim 10, wherein the optical waveguide layer has a cross sectional formation so that a cross sectional width of the optical waveguide layer becomes wider as a distance from the surface of the TFT substrate increases; and wherein a height of the tilted metal surface from the flat surface portion of the light-emitting element is larger than a maximum height of the optical waveguide layer.
 12. The display device according to claim 8, wherein inactive gas is arranged in the gap.
 13. The display device according to claim 9, wherein the first and the second banks are formed in an integrated manner; wherein a peripheral region of the anode surrounds the flat surface portion of the light-emitting element in plan view; and wherein the first bank is arranged between the first metal surface and the peripheral region of the anode, and the second bank is arranged between the second metal surface and the peripheral region of the anode.
 14. The display device according to claim 13, further comprising: a plurality of driver elements each connected to each of the light-emitting elements; a plurality of capacitor elements each of which is connected to each of the light emitting elements and receives each of a plurality of image signals; and a plurality of switching elements each of which is connected to one of the capacitor elements and one of the light emitting elements and controls input of one of the plurality of image signals to one of the capacitor elements; wherein the insulating layer has a contact hole formed on the driver element; wherein the anode is formed on the insulation layer; wherein the peripheral region of the anode is connected to the driver element via the contact hole; wherein the first bank is formed to cover the contact hole.
 15. The display device according to claim 13, wherein the first metal surface is provided on a peripheral area surrounding the flat surface portion of the light-emitting element and has a first tilt angle with respect to the flat surface portion of the light-emitting element; wherein the second metal surface is provided in the peripheral area surrounding the flat surface portion of the light-emitting element and has a second tilt angle with respect to the flat surface portion of the light-emitting element; and wherein the first and the second banks includes the peripheral area formed on the peripheral region of the anode.
 16. A display device including a plurality of light-emitting elements aligned on a TFT substrate in a formation of a matrix, wherein the display device comprises: at least one of the plurality of light-emitting elements having a flat surface portion and including an organic layer, an anode and a cathode; an insulation layer formed on the TFT substrate and under the light emitting element; a metal surface is provided on a surface of an insulation bank that is provided on the insulating layer; wherein each of the insulating bank and the metal surface surrounds the flat surface portion of the light-emitting element in plan view; wherein a width of a cross section of the insulation bank becomes smaller as the cross section comes farther away from a surface of the TFT substrate; wherein a counter substrate is placed on the TFT substrate; and wherein gap exist between the light emitting element and the counter substrate.
 17. The display device according to claim 16, wherein the anode, the organic layer including a light-emitting layer, and the cathode is arranged in this order; wherein at the flat surface portion of the light-emitting element, the anode is connected to the organic layer, and the organic layer is connected to the cathode.
 18. The display device according to claim 17, wherein a peripheral region of the anode surrounds the flat surface portion of the light-emitting element in plan view; and wherein the insulation bank is arranged between the metal surface and the peripheral region of the anode.
 19. The display device according to claim 16, further comprising: a plurality of driver elements each connected to each of the light-emitting elements; a plurality of capacitor elements each of which is connected to one of the light emitting elements and receives each of a plurality of image signals; and a plurality of switching elements one of which is connected to one of the capacitor elements and one of the light emitting elements and controls input of one of the plurality of image signals to one of the capacitor elements; wherein the insulation layer has a contact hole formed on the driver element; wherein the anode is formed on the insulation layer; wherein the peripheral region of the anode is connected to the driver element via the contact hole; and wherein the insulation bank is formed to cover the contact hole.
 20. The display device according to claim 18, wherein the metal surface is provided on a peripheral area surrounding the flat surface portion of the light-emitting element and has a tilt angle with respect to the flat surface portion of the light-emitting element; and wherein the insulation bank includes the peripheral area formed on the peripheral region of the anode. 